As shown in FIG. 1, a hybrid vehicle according to the related art includes a mechanical oil pump (MOP) 10 which rotates together with an engine 1 and a motor 2, and an electric oil pump (EOP) 20 which is operated by the electric motor. Among these, the MOP 10, which is a main configuration providing oil pressure to a transmission 3, or the like, is interlocked with a rotational shaft of the engine 1 or the motor 2 to be operated.
That is, the hybrid vehicle according to the related art includes a system in which the MOP 10 is operated together to generate the oil pressure while the engine 1 or the motor 2 runs, and the EOP 20 is additionally operated to assist the oil pressure when a flow rate of oil is insufficient.
However, since the MOP 10 is operated by driving force of the engine 1 and the motor 2, it disturbs driving of the vehicle, thus decreasing fuel efficiency. Further, the MOP has become big obstacle in improving fuel efficiency.
Thus, there has been an attempt to improve the fuel efficiency by removing the MOP and forming the oil pressure using only the EOP. However, in order to form the oil pressure by only the EOP, since the oil pressure of the MOP is supplied through only the EOP, there is a need to significantly increase revolutions per minute (RPM) of the EOP. However, since the EOP is separately installed outside the transmission, when the RPM of the EOP increases, noise generated from the EOP is directly delivered to passengers.
In addition, when an oil temperature increases, an oil leak amount increases as viscosity of oil decreases. In order to increase a supply amount of oil for compensating for the increased oil leak amount, the RPM of the EOP should increase.
In addition, high oil pressure is required to smoothly exchange a gear when shifting. In order to realize the high oil pressure, the RPM of the EOP should increase.
A maximum RPM of the EOP used together with the MOP is about 2500 RPM. However, when only the EOP is used, the EOP rotates at a high speed of about 3500 RPM, where passengers may recognize noise.
Noise may increase as the RPM of the EOP increases when using only the EOP.
Therefore, a method of improving riding quality by suppressing noise occurrence of the EOP in a situation in which passengers may recognize noise has been demanded.
A method for controlling an oil pump of a hybrid vehicle has been studied. According to this method, an RPM of an electric oil pump increases by determining a manipulation from an N stage to a D stage, and after a predetermined time lapses, the RPM of the electric oil pump decreases. Noise occurrence is prevented by controlling the RPM of the electric oil pump as described above.
However, the above-mentioned related art relates to the method for controlling the hybrid vehicle according to the related art in which the MOP as well as the EOP are installed, and has a limitation in that it does not disclose a method for controlling RPM of the EOP depending on oil temperature, RPM of the engine, or the like.